1. Technical Field
Example embodiments of the present invention relate in general to the field of polymer solar cells, and more specifically to a photoactive layer composite in which a silica thin film layer is formed between an electron donor layer and an electron acceptor layer, and a polymer solar cell using the same.
2. Related Art
A solar cell is a photonic device that generates electrons and holes to generate photovoltaic power from incident sunlight. A solar cell may be classified as an inorganic solar cell or an organic solar cell, according to the type of material that absorbs incident light to form excitons.
An inorganic solar cell is a silicon-based solar cell in which an inorganic material is formed in a deposition process, and electrical energy is generated from the stacked structure thereof. Inorganic solar cells have already been commercialized, and show high power conversion efficiency compared to other solar cells. However, there is a limit in application thereof due to properties of the inorganic materials. For example, the installation is possible in limited outdoor spaces, and since the inorganic solar cell has no flexibility, the direction of the solar cell needs to be modified depending on the incident angle of sunlight. In addition, high manufacturing costs are incurred due to limited reserve of materials and high material costs of thereof.
An organic solar cell uses an organic material as the photoactive layer. An organic solar cell is classified as a dye-sensitized solar cell or a polymer solar cell according to the type of the organic material. A polymer solar cell includes a photoactive layer in which an electron donor material and an electron acceptor material are mixed. A polythiophene (P3HT) polymer may be used as the electron donor, and fullerene may be used as the electron acceptor. The two materials are not completely mixed but formed to have several tens of nanometers of fine grains through phase separation, and have mutually three-dimensional random structures. The photoactive layer absorbs sunlight to generate excitons. The excitons are dissociated from an interface between the electron donor material and the electron acceptor material to be separated into electrons and holes, and the charges move to respective electrodes.
A polymer solar cell may have a structure in which an electrode and a photoactive layer are sequentially stacked. However, efficient moving and storing operations of separated charges are required between a plurality of distinguishably stacked layers. In order to achieve this, studies on inserting a functional interfacial layer between each electrode and the photoactive layer are being conducted.
The inserted interfacial layer is formed between the photoactive layer and the electrode, and solves the problem caused by a difference in a work function between the photoactive layer and the electrode, or increases the efficiency by generating appropriate dipole moments for moving charges in each electrode. In addition, the interfacial layer, such as TiO2, ZnO, polyethylene glycol, or polyfluorene derivatives, prevents electron-hole recombination at an interface between the electrode and the photoactive layer.
However, since the above described interfacial material or interfacial layer is not formed inside the photoactive layer in which a photochemical process actually occurs, the interfacial material or interfacial layer may not control an internal operation of the photoactive layer, and may be stacked above or below the photoactive layer to control a moving or storing operation of already-generated electrons or holes in the electrode.
That is, there is a limit in that conventional methods of improving light-to-electric energy conversion efficiency may not control loss caused by the electron-hole recombination in the photoactive layer, and may function only to ease the movement of charges between the photoactive layer and the electrode. This is because the interface between the electron donor material and the electron acceptor material has an irregular three-dimensional microstructure, and therefore interfacial characteristics may not be controlled through a general stacking method.